Move runtime interfaces to runtime package

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

runtime/runtime.go

@@ -0,0 +1,47 @@
+package runtime
+
+import (
+	"context"
+	"time"
+
+	"github.com/containerd/containerd/mount"
+)
+
+type IO struct {
+	Stdin    string
+	Stdout   string
+	Stderr   string
+	Terminal bool
+}
+
+type CreateOpts struct {
+	// Spec is the OCI runtime spec
+	Spec []byte
+	// Rootfs mounts to perform to gain access to the container's filesystem
+	Rootfs []mount.Mount
+	// IO for the container's main process
+	IO         IO
+	Checkpoint string
+}
+
+type Exit struct {
+	Pid       uint32
+	Status    uint32
+	Timestamp time.Time
+}
+
+// Runtime is responsible for the creation of containers for a certain platform,
+// arch, or custom usage.
+type Runtime interface {
+	// ID of the runtime
+	ID() string
+	// Create creates a task with the provided id and options.
+	Create(ctx context.Context, id string, opts CreateOpts) (Task, error)
+	// Get returns a task.
+	Get(context.Context, string) (Task, error)
+	// Tasks returns all the current tasks for the runtime.
+	// Any container runs at most one task at a time.
+	Tasks(context.Context) ([]Task, error)
+	// Delete removes the task in the runtime.
+	Delete(context.Context, Task) (*Exit, error)
+}